1. Field of the Invention
This invention relates to an apparatus inserted in the body cavity of a patient, for receiving nuclear-magnetic resonance signals of the living body of the patient in a static magnetic field, which signals are generated by applying high frequency energies to the living body, in use with an MRI system.
2. Description of the Related Art
There has recently been developed a non-attacking diagnosing method for a human body which utilizes a nuclear-magnetic resonance phenomenon (the nuclear-magnetic resonance being hereinafter referred to as the "MR"). With a magnetic resonance imaging device (the magnetic resonance imaging being hereinafter referred to as the "MRI"), a human body is placed in a static magnetic field, and a predetermined high frequency magnetic field is applied to the human body to excite nuclei having spins of the tissues in the body cavity of the human body. MR signals having a predetermined frequency produced until the excited nuclei return to the original positions are detected and processed by a computer to obtain cross-sectional images of the body cavity of the human body.
The cross-sectional images obtained by the MRI device are extremely effective for diagnosis such as distinction of abnormal cells such as cells suffering from cancer from normal cells. It is known that MR signals from cancer tissues and normal tissues are generated at different relaxation times. Therefore, it is possible to diagnose whether the living tissues to be examined are suffering from cancer or not by measuring and imaging the MR signals based on the relaxation time, without picking them up.
Fine and accurate images must be obtained to diagnose diseases of the digestive system such as a tubular viscus and particularly to find the depths of its affected portions. However, since the MR signal receiving coil is provided externally of a patient body with the conventional apparatus, it is difficult to obtain fine and accurate cross sectional images of deep portions of the tubular viscus of the patient. For example, with a conventional system, a surface coil for receiving MR signals is placed on the abdomen of a patient and receives MR signals to diagnose the stomach walls. However, the signal-to-noise ratio (hereinafter referred to as the "SN ratio") is too low to obtain images sufficient for required diagnosis.
In order to overcome this problem, there has been proposed an insertion apparatus such as an endoscope or a probe, which is provided, on the distal end of an insertion section inserted in the body of a patient, with an MR signal receiving high frequency coil, for detecting MR signals, as disclosed in Published Examined Japanese Patent Application No. 3-5174 and Published Unexamined Patent Application No. 2-277440. With them, a coil inserted in the patient's body receives MR signals and provides fine and accurate images having a good SN ratio. Thus, fine and accurate images can be obtained for diagnosing the depths of affected portions of tubular viscus.
when an MR signal receiving high frequency coil is provided on the distal lend portion of the insertion section, it is demanded that the opening of the high frequency coil be made as large as possible. For example, the scanning range swept by the MRI device is widened when the coil opening is rectangular and long, and the SN ratio is improved when the area of the coil opening is large. These features give advantages to MR diagnosis.
In case, however, when an observation optical system, an illumination optical system and the like are assembled into the distal end portion of the endoscope insertion section inserted in the patient's body, the outer diameter of the distal end portion of the endoscope insertion section and the rigid part of the distal end portion become large. Thus, the conventional MR endoscope in which the MR signal receiving coil is provided gives a heavy burden to the patient.
It is, therefore, demanded that technology should be developed for assembling an MR signal receiving coil, in a compact manner, into the insertion portion of an insertion instrument such as an endoscope or a probe which should be thin for relieving a burden to the patient.